Crazy ants take on fire ants and win

Crazy enough to use their own venom to detoxify that of a fire ant.

If you’ve ever been attacked by red imported fire ants, you can likely attest that these tiny insects have a nasty defense mechanism. When threatened, fire ants inject or dab their enemy with a potent neurotoxic venom that quickly dispatches most other ants and can sometimes even send humans to the hospital.

This deadly assault is a pretty effective deterrent to most other ant species, which tend to keep their distance. But the fire ants have now run up against another invasive species that's willing to take them on: the tawny crazy ant. This unassuming little ant has the surprising habit of aggressively barreling right into a colony of fire ants, seemingly undeterred by their toxic venom.

In this week’s issue of Science, researchers from the University of Texas at Austin report that crazy ants are actually able to detoxify fire ants’ venom, helping them displace this usually dominant species.

A crazy ant’s headlong charge into a mass of fire ants almost always results in it being smeared with venom. But once covered in the neurotoxin, these ants perform a systematic and ritualized behavior. First, an ant stands on its hind legs and curls up its abdomen, touching its mandibles to a small gland at the tip of its body called the acidopore. The ant then runs its front legs through its mandibles and grooms itself fastidiously.

It looks like the ant is covering itself with a secretion from its own body as a response to the fire ant's venom. To determine whether this behavior actually counteracts the venom’s effect, the researchers ran a controlled test. They used nail polish to seal the acidopore of one group of crazy ants, and simply sham-treated a second control group. After coming into contact with fire ant venom, the crazy ants with the sealed acidopores—which could not secrete any chemical defenses—had a survival rate of just 48 percent, whereas 98 percent of the control group survived. Clearly, something originating from the acidopore was increasing the survival of ants covered in venom.

By testing crazy ant secretions, the researchers found that the life-saving substance was actually formic acid from the crazy ants’ own venom. So far, it's unclear exactly how this chemical detoxifies fire ant venom. It’s possible that formic acid denatures the enzymes that enable neurotoxins to enter cells.

While this rare ability confers a huge advantage for crazy ant survival, its biggest implications are ecological. Ever since fire ants were imported into the southern US in the 1930s, they have been the dominant ant species in most grassland ecosystems. But crazy ants—introduced only about 12 years ago—are now taking over, thanks in part to their ability to detoxify fire ant venom. When the two species fight over food or space, crazy ants come out on top 93 percent of the time.

Digging into these two species’ past sheds light on this asymmetry. Tawny crazy ants and red imported fire ants share an evolutionary history since their native ranges overlap in parts of South America. Their arms race began there, with fire ants evolving venom to defend themselves and crazy ants evolving a detoxification mechanism as a counter-defense. Now the chemical warfare has been re-engaged here on a second continent, playing out across the Gulf Coast. And for a second time in the past century, a new invasive ant species is dominating and drastically transforming ecological communities.

Related PSA: crazy ants are attracted to electronics. So if you're a technology lover living in the southeastern US, watch your computers and appliances because these tiny invaders are headed your way.

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Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida